This invention relates to a balloon catheter for use in delivering a medical device such as a stent to a desired body location, such as in a blood vessel. More specifically, this invention relates to a stent mounting region on a balloon catheter which has multiple balloon elements while are separated by spaces. Contained within the spaces between the balloon elements are stent mounting bodies which extend radially and act to receive and secure a stent, in its pre-delivered crimped form, to the balloon catheter.
In balloon expansion of a stent it is important that the stent be accurately positioned over the body portion of a balloon. Failure to properly position the stent over the balloon may result in an unintended non-uniform expansion of the stent. Furthermore, improper positioning of the stent with respect to the balloon during inflation may result in improper final placement of the stent within the body vessel. Failure to keep the stent securely positioned during balloon expansion may cause the expanded stent to shift in position or drift within the vessel prior to the final seating of the expanded stent.
The present invention addresses the above problems by ensuring proper securement and positioning of the stent over the balloon throughout the expansion process by utilizing a segmented balloon or multiple balloon elements respectively interspaced with a stent mounting body or bodies.
It is well known in the stent delivery art that a stent delivery apparatus, such as a balloon catheter, should have as low a profile as possible. However, due to the design and construction of many stents, the delivery apparatus will often require that additional protective layers be added to the catheter in order to protect the expansion balloon from being damaged by the stent during inflation, as well as to protect the anatomy of the vessel from being hooked or torn by the stent as it is inserted into the body. As such, numerous delivery catheters have employed multiple layer balloons, and complex sheath arrangements all of which undesirably increase the diameter of the delivery catheter.
One such multiple layer balloon catheter for delivering a stent is U.S. Pat. No. 5,807,327 to Green et al (Green), incorporated herein by reference. Green discloses a stent delivery catheter having a balloon (126) with three layers. A first or inner layer (138) is a burst resistant layer which has a second layer (140) disposed exteriorly of the first layer (138). Because of problems associated with the high coefficient of friction of the second layer (140) a third layer (142) may be wholly or partially added to the second layer (140). Green uses an excessive number of balloon layers to ensure that the balloon is uniformly inflated. The multiple layers of Green and other similar multiple layer balloon catheters have a greater profile than is desirable.
U.S. Pat. No. 5,647,857 to Anderson et al (Anderson), which is incorporated herein by reference, discloses a sheath for holding a device in a desired position against a balloon catheter for delivery in the lumen of a patient. By adding a sheath such as that which is shown in Anderson, an additional layer is added to the balloon catheter thereby undesirably increasing the profile of the catheter.
The present invention provides a low profile catheter capable of properly expanding and seating a stent. The low profile balloon catheter of the present invention utilizes one or more stent mounting bodies to secure the stent to the catheter, the bodies being arranged so that the balloon has minimal contact with the potentially sharp edges of the stent. The stent mounting bodies of the present invention provide the feature of ensuring that the stent is accurately and securely positioned on the balloon catheter with respect to the balloon, thereby ensuring proper expansion and positioning of the stent during balloon inflation.
The present invention is directed broadly to a balloon catheter including a stent mounting body or bodies which receive the stent distally, allowing the balloon to avoid distal contact with the unexpanded stent.
The stent mounting bodies may be designed to mate with the open structures typical of most stents. The stent mounting bodies may be individually configured on a stent-by-stent basis to mate with the numerous and often uniquely shaped open structure typical of stents. The stent mounting bodies may be configured to act as simple supports or guides for the stent during inflation thereby preventing the stent from shifting position during expansion. Furthermore, by mounting the stent directly to the stent mounting bodies, as opposed to mounting the stent upon a balloon having internal mounting bodies, allows the balloon to avoid the potentially sharp edges of the stent""s open structures which could otherwise rupture the balloon prior to or during inflation. The stent mounting bodies may also be configured to form a mechanical lock with the open structures of a given stent type, or form a lock that selectively releases portions of the stent during expansion.
The stent mounting bodies may be comprised of a compressible or elastic material so as to deform under the stent to provide support and holding for it.
In order to accommodate the presence of stent mounting bodies along the central shaft of a catheter, the balloon is formed in multiple individual balloon elements with spaces between each balloon element. The balloon elements may be individual balloons per se or segmented portions of a single balloon or any combination thereof. The stent mounting bodies are located within the spaces that separate the balloon elements. The stent mounting bodies extend radially away from the catheter.
The stent receiving portion(s) of the stent mounting bodies may be configured with unique end caps or heads which will act to form mechanical locks with the individual spaces of the stents to which the stent mounting bodies are mated. When the balloon elements are fully inflated the stent is forced off of the stent mounting bodies as the balloon pushes the stent away from the catheter. The balloon elements will preferably surround and overlap the stent mounting bodies when fully inflated. The fully expanded balloon elements will seat the stent into its final position against the vessel wall.
The balloon elements may be configured to act as individual balloons thereby allowing the operator the ability to expand selected portions of the stent, such as for example, the central portion of the stent first, in order to reduce the potential for flaring along the stent ends. Such selective inflation could also be used to increase pressure on areas of the stent that are interfered with during expansion due to the presence of plaque or other common interferences.
When the balloon elements are deflated the catheter may be withdrawn. The stent mounting bodies may be constructed to be readily flexible or collapsible so as to not interfere with the anatomy of the vessel as the catheter is being withdrawn, although this is not necessary.